body {
  margin: 0;
}

ul {
  display: flex;
  justify-content: space-around;
  width: 500px;
  padding: 0;
}

li {
  list-style: none;
  height: 30px;
  line-height: 30px;
  text-align: center;
  width: calc(100% / 3);
  background: #ccc;
  color: aquamarine;
}

li.active {
  background: indianred;
  color: antiquewhite;
}
.tags > div {
  width: 500px;
  height: 480px;
  border: 2px dotted #ccc;
  display: none;
}
.tags > div.active {
  display: block;
}


.box{
  width: 200px;
  height: 200px;
  background: red;
  position: fixed;
}